The present invention relates to an improved tubular casing, and more especially to a tubular casing for foodstuffs, especially sausages, which is composed of fiber-reinforced regenerated cellulose wherein a web of fibrous material is curved longitudinally to form the tube and the edges are bonded together. The present invention also relates to a process for the manufacture of such casings.
Tubes of this type, composed of fiber-reinforced regenerated cellulose, are customarily manufactured (see, e.g., U.S. Pat. Nos. 2,144,900, 3,224,885, 3,645,760 and 4,195,054) by the following essential process steps. A web of non-woven fiber is formed into a tube, its edges are overlapped and then glued with viscose. After coating of the entire tube surface with viscose, on one side or on both sides, for example, from annular slot dies, the viscose is coagulated and regenerated to give cellulose hydrate gel, and the product is dried. During this process, the tube is supported by the gas mixture formed during the coagulation and regeneration and, during drying, it is supported by an enclosed volume of air, which has been introduced. If appropriate, the tube is stretched in the longitudinal and transverse directions in order to improve the mechanical properties.
In this procedure, some disadvantages must be accepted. In particular, this process is very cost-intensive. Moreover, the internal coating of such a tube is very involved and expensive to carry out.
A further essential disadvantage of this process is the discontinuous course of production, caused by the accumulation of gases and liquids in the interior of the tube during the regeneration stage. These must be removed from the interior of the tube at certain intervals. For this purpose, the tube is cut open and the cutting points are removed after the tube has run through the wet section. The tube ends formed by the cutting-open are then joined together again, for example, by means of viscose and subsequent action of heat (German Offenlegungsschrift No. 1,814,590), so that a continuous tube is present again in the final drying stage. A further cause of the discontinuous nature of the process is the introduction of coating fluid into the interior of the tube before and after the drying stage. To do this, the tube is initially cut open in the same way and then is completely resealed after filling.
On the other hand, a process is also known (U.S. Pat. No. 2,653,432) in which the overlapping edges of a film which is curved into the shape of a tube and which, for example, can also be composed of regenerated cellulose with optional fiber reinforcement, are glued together by means of a strip of thermoplastic material, which strip is located between the overlapping edges and becomes tacky on heating. Acrylate and polyvinylidene chloride are mentioned, inter alia, as examples of this thermoplastic material. This known tubular casing can also have a moisture-tight coating on the outside, with the overlapping edges then being kept free of coating and the remaining surface being kept free of thermoplastic material.
In this process, the adhesive is thus intended to be present not directly on the fiber reinforcement, but on the web surface composed of regenerated cellulose, and, for this reason, it is not used for gluing the overlapping edge zones of the fiber reinforcement. Moreover, the strength of an overlapping seam formed by sealing of the superposed edge zones of regenerated cellulose is comparatively low and is also completely unsatisfactory for reasons of appearance.